A pressure vessel for storing high pressure gaseous mediums (such as hydrogen, compressed natural gas, or air) typically include an inner plastic liner, at least one mouthpiece (metal boss), and a wound outer shell to support the pressure vessel. The pressure vessel may be incorporated into a vehicle to supply hydrogen to a proton exchange membrane (PEM) fuel cell stack capable of powering the vehicle, for example. Hydrogen stored within the vessel may be pressurized to at least 70 MPa to accommodate a travel range of the vehicle consistent with consumer needs. Accordingly, adequate sealing between the inner plastic liner and the at least one boss is necessary to militate against loss of the gaseous medium.
The inner plastic liner may be produced by any conventional process such as rotational molding, blow molding, injection molding, or thermoforming. As examples, the following patents disclose pressure vessels including an inner liner (WO 1999/039896; WO 2007/079971; DE 19526154; and WO 1999/013263), each of which is incorporated herein by reference in its entirety.
The gaseous medium passes through the boss when one of entering and exiting the pressure vessel. The boss is typically configured with one of threads or other coupling means to accept a valve, a sensor, a coupler, a conduit, or other device. Accordingly, the boss provides a reliable and versatile coupling point for the pressure vessel.
Sealing elements such as a compression fitting and O-rings may be disposed between the boss and the inner plastic lining to militate against an unintended loss of the gaseous medium. Multi-piece boss designs, a plurality of sealing elements, or compression of the lining by the boss may be used to form a seal between the inner plastic lining and the boss.
U.S. Pat. No. 7,032,767 discloses a multi-piece boss design for a pressure vessel including an inner plastic lining, wherein a seal is disposed between the boss and the lining. In addition to requiring a complicated assembly procedure, the multi-piece boss design does not accommodate fluctuating forces exerted on the seal caused by repeated thermal cycles and pressure cycles. For example, a high pressure and temperature of the fluid within the pressure vessel causes the inner plastic lining to increase in size to an expanded state, increasing a force exerted by the seal on the boss and the liner. Conversely, a low pressure and temperature of the fluid within the pressure vessel causes the inner plastic lining to retract in size from the expanded state, decreasing a force exerted by the seal on the boss and the liner.
Movement of the boss with respect to the inner plastic lining in the pressure vessel is an undesirable effect that may occur during one of assembly and use of the pressure vessel. Particularly, one of an axial and a rotational movement of the boss may cause a fluctuation of the forces exerted on the seal. The axial movement of the boss may permit one of the boss and a boss component to fall inside the pressure vessel or separate from the pressure vessel. Further, the axial movement of the boss may separate the seal from contact with one of the boss and the lining. The rotational movement of the boss may permit one of the boss and the boss component to disengage from a fastening means and exert a localized force on at least a portion of the seal.
The seal disposed between the boss and the lining may be improperly positioned due to an inability to visually confirm a proper placement of the seal. The seal incorporated in the multi-piece boss may not be visible during the assembly of the pressure vessel. As a result, the seal may be improperly positioned or subject to an unintended force during the assembly. Additionally, the pressure vessel may include the boss that is permanently affixed to the lining by one of an adhesive and the wound outer shell. As a result, a service life of the seal may be shorter than a service life of the pressure vessel.
It would be desirable to develop a boss and a capture sleeve for use with a pressure vessel, wherein proper installation of a seal disposed between the boss and a lining of the pressure vessel is facilitated and the sleeve and the lining militate against movement of the boss, and wherein the boss facilitates installation and replacement of the seal.